1. Field of the Invention
The present invention relates to a conductive glass, and is particularly concerned with a conductive glass having a high strength and a high wear resistance.
2. Description of the Prior Art
Lately, a conductive glass is used in various fields such as electrodes for various displays or thin film photoelectric cells, transparent touch sensor, transparent anti-static coating, transparent electromagnetic shield and the like. The conductive glass is obtained exclusively by coating a glass substrate with a transparent conductive coating material thereon. For this kind of material, an oxide material having a semiconducting function is employed preferably, which includes representatively stannic oxide, indium tin oxide (hereinafter referred to as ITO), zinc oxide, cadmium tin oxide and others.
Since the conductive glass is exposed usually to a working surface, a high wear resistance and chemical resistance (acid and alkali resistances) are required sometimes for particular service. Further, for safety, there may be a case where a strength remarkably higher than a normal plate glass is required with the glass itself. To obtain a glass plate with high strength, such glass heated up to a softening point or over is cooled down quickly from the surface thereof to obtain a compression stress which is normally called thermal tempering, or glass plate is soaked in a molten salt containing potassium ion to exchange with a sodium ion in the glass, and thus the surface compression stress is obtained according to a difference in size of the ions, which is called chemical tempering. In either case, the glass is exposed to high temperature at about 400.degree. C. to 600.degree. C. in a process for increasing a strength of the glass.
However, it was difficult so far to satisfy concurrently an electrical characteristic of the conductive glass, a mechanical strength of the coat and a strength of a glass substrate. For example, an ITO film typical as the transparent conductive film displays a superior electrical characteristic, but is weak in wear resistance and chemical resistance of the film, and in addition a problem inherent therein is such that the electrical characteristic deteriorates or the film is damaged by carrying out the thermal tempering or chemical tempering for obtaining a strength of the conductive glass.
On the other hand, a stannic oxide film is superior to the ITO film in wear resistance. However, if a strength of the conductive glass is increased through the thermal tempering, then a sudden change in temperature of the process may often cause a crack on the film or a severe deformation of the glass substrate. Accordingly, for the thermal tempering, a strict temperature control will be necessary, or a deterioration of productivity may occur sometimes.
Further, it is conceivable that the glass substrate with thermal tempering and chemical tempering applied thereon beforehand is coated with a transparent conductive film, however, if a coating temperature is high in this case, the surface compression stress layer will vanish due to a transfer or diffusion of atoms.
Accordingly, a method available for coating at low temperature after the tempering is applied (for example, vacuum deposition and sputtering) is preferable as means for obtaining a conductive glass having a satisfactory strength, however, the equipment of this kind requires vacuum, so that a coating cost gets high inevitably.